Many of today's toddlers face the grim prospect of coping with chronic food shortages in their old age if agricultural science doesn't adapt to a warming world, concluded scientists in a study published Friday in the journal Science.

The stark report, from scientists at Stanford University and the University of Washington, makes melting polar ice caps and rising sea levels from global warming appear minor compared with the prospect of hundreds of millions of people, including those living in Europe and the United States, anxiously seeking stable food supplies.

Global warming's effect on food production, said David Battisti, professor of atmospheric sciences at the University of Washington and lead author of the study, is one of "the foremost reasons" for concern about climate change. The study's co-author is Rosamond Naylor, director of Stanford University's Program on Food Security and the Environment.

By the end of the century, the worst of the heat waves in recent times will become the normal average summertime temperatures, the researchers reported. They based their conclusions on 23 climate models in a 2007 report from the Intergovernmental Panel on Climate Change, as well as data from severe heat waves dating several decades.

There's a 90 percent probability, Battisti said, that by 2100, typical growing season temperatures in the tropics and the subtropics would exceed the most extreme seasonal temperatures recorded from 1900 to 2006. Those regions lie between 35 degrees latitude north and south, and include the Southeast and Southwest United States, southern Europe, Central America, northern Australia, as well as Africa and large swaths of India and China. About 3 billion people, or half the world's population, live in these regions — a figure expected to double by 2100.

Battisti and Naylor also based their estimate on assumptions that greenhouse gas emissions would level off by midcentury, and then begin declining. That scenario would lead to an approximate doubling of CO2 levels by the end of the century, he said.

"If anything, we took the most conservative approach," Battisti said.

In addition, they didn't account for anticipated lower rainfall levels from climate change, or the spread of pests and pathogens attacking vulnerable, heat-stressed plants.

"So everything we neglected (to account for) seems to make things worse," he said.

The scientists said yields of staple crops such as rice and corn could fall by 20 percent to 40 percent by the end of the century, as temperatures rise an average of 6 degrees during the growing seasons.

In their article, Battisti and Naylor cited the 2003 heat wave in Western Europe to illustrate the potential effects of these higher temperatures. That extreme summer heat killed more than 50,000 people and cut some crop yields by a third. Such summer temperatures in the region would become the norm under the scientists' scenario.

Battisti said these findings, in his view, call for far more serious action to reverse global warming trends.

But given the challenges in achieving such a reversal in the near term, he said it's imperative that agricultural research priorities shift beyond only producing drought-resistant plants, to ones that can maintain productivity even in high heats.

In addition, more sophisticated trading systems would need development, he said, to distribute foods from areas with more productive farmlands to areas affected by rising heat.

"The main thing we're talking about is really large adaptations, or moving hundreds of millions of people," he said.

Reach Suzanne Bohan at 510-262-2789 or sbohan@bayareanewsgroup.com.